The present invention relates to a continuous process for preparing bisfluoroxydifluoromethane, hereinafter designated as "BDM", which comprises reacting carbon dioxide with fluorine in the presence of a cesium fluoride catalyst.
Bisfluoroxydifluoromethane is a useful reagent for chemical synthesis reactions such as direct aromatic fluorination reactions. In such aromatic substitution reactions, the reaction of BDM with a suitable aromatic substrate results in the addition of a fluorine atom to the aromatic nucleus. This may result in the formation of unique fluorinated aromatic compounds which cannot be readily prepared using more conventional fluorinating agents. As illustrated by the foregoing, BDM is a useful reagent which has potential commercial applications in many organic synthesis reactions.
Bisfluoroxydifluoromethane has been previously prepared using a variety of methods. One method involves the fluorination of sodium trifluoroacetate and has the disadvantage of low yields and expensive reactants. Another method reacts fluorine with an alkali metal oxalate, such as sodium oxalate, in the presence of an alkali metal or alkaline earth metal fluoride. See the disclosure in U.S. Pat. No. 3,394,163. This method requires low temperature conditions for both the reaction and separation of BDM from reactants. In addition, this reaction also suffers from low product yields, and alkali metal oxalates are comparatively expensive for commercial processes. See, for example, P. G. Thompson, Journal of the American Chemical Society, Vol. 89, pages 1811 and 1813 (1967), which also describes the fluorination of sodium oxalate using the static bed process. Product yields of only 1% to 15% of BDM were achieved using this process.
A number of other processes are reported in the literature for preparing BDM. An article by F. A. Hohorst and J. M. Shreeve appearing in Inorganic Synthesis, Vol. 11, pages 143-147 (1968), describes the preparation of BDM by the static fluorination of carbon dioxide in the presence of anhydrous cesium fluoride at -78.degree. C. Low temperature reaction conditions are required to preclude the formation of CF.sub.3 OF and OF.sub.2. The reaction requires approximately six hours and is carried out in an autoclave under essentially static conditions. In addition, a substantial excess of fluorine is required, e.g. nine moles of fluorine per mole of carbon dioxide. A related article by F. A. Hohorst and J. M. Shreeve appears in the Journal of the American Chemical Society, Vol. 89, pages 1809-10 (1967).
It is therefore a primary objective of the present invention to provide a continuous process for producing BDM in high yield using relatively mild reaction conditions.